DURHAM, N.C. — As the fury of Hurricane Sandy crashed into the Northeast last month, online postings along the storm’s path recounted the collapse of one service after another — no lights, no heat, no phones, no subway and, ultimately, no Internet. But amid the darkened buildings and flooded subways of Lower Manhattan, one service remained largely intact and, as a result, largely ignored: the water supply. As Mayor Michael Bloomberg confidently tweeted, “NYC Tap Water is absolutely safe to drink.”

The media hardly noticed. We take easy access to reliable, clean drinking water for granted. But it hasn’t always been that way: Lack of safe drinking water has plagued American cities for most of their history. In fact, what’s truly remarkable is that the one problem New York did not face after Sandy was contaminated water.

But the drinking water in New York and other American cities remains under serious threat from sources both less obvious and less direct than natural disasters.

For starters, the system’s infrastructure is decaying. Nationwide, more than 10 percent of public water is lost through leaks. On average, a major water pipe bursts somewhere in the country every two minutes. In Washington, D.C., a pipe bursts every day.

This should not be surprising. Most of our water systems were built decades ago. Some date to the Civil War. The EPA estimates that $335 billion will be needed simply to maintain the current water infrastructure over the next few decades. Upgrades would cost even more.

So what are we doing about it? To date, very little. We are starving our water system of funds and have been doing so for years. Part of the reason is the system’s invisibility; the average citizen doesn’t give buried water pipes a thought until they burst and faucets run dry. Another part is a lack of public understanding of how antiquated our infrastructure has become. Finally, there is a stubborn refusal to pay for the system’s actual cost; we seem to think it has always been cheap and should remain so, come hell or high water.

And because of climate change, both hell and high water may be in store for us. In addition to making water more scarce in some regions of the country — pitting cities’ consumption against agricultural demands — climate change will give rise to storms of greater intensity, according to most models. Sandy’s uncommon power could become the new reality, placing public services under regular threat of deluge. We may have no choice but to harden our infrastructure as “hundred-year” storms become commonplace.

A further challenge, even more difficult to assess, comes from emerging contaminants. We are introducing compounds into our environment that did not exist only a few decades ago. To take one example, millions of people ingest pharmaceutical products every day, treating a range of conditions from arthritis to depression. Our bodies excrete residue from the drugs into the sewage system, and unused medications are often flushed down the toilet. As a result,they turn up in our tap water. One study found evidence of 56 pharmaceuticals or their byproducts in treated drinking water, including in metropolitan systems that together serve more than 40 million people.

These drugs are designed to change human body chemistry, and the risks they pose in the water supply may be real, but they are hard to quantify. The concentrations are extremely low, sometimes in parts per billion or even parts per trillion — far, far below the level of a prescribed medical dose. Nor are there any documented cases of pharmaceutical traces in drinking water leading to harm, but with such small doses it is difficult to assess effects that may be subtle or distant in time. As EPA scientist Christian Daughton has described, such contaminants are “at the outer envelope of toxicology.”

Other emerging contaminants, such as methane from fracking and endocrine disruptors from pesticide runoff, raise similar concerns.

Despite these challenges, it’s important to recognize the scale of achievement in a clear glass of tap water. We can go to any city in the United States and sip from a fountain without a moment’s concern for our health. This is remarkable, and it certainly was not inevitable. For most of human history, and in many parts of the world today, clean drinking water has not been readily available or expected.

James Salzman, an environmental law professor at Duke University, is the author of “Drinking Water: A History.” He wrote this column for the Washington Post. His email address is salzman@law.duke.edu

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